Human Proteinase-Activated Receptor 1 (hPAR1), also known as thrombin receptor, is a 65-70 kDa, 399 amino acid long member of the seven-transmembrane superfamily of cell-surface G protein-coupled receptors. PAR1 is activated by thrombin cleavage of its N-terminal propeptide in the extracellular domain. Human PAR1 is widely expressed in many cell types including endothelial cells, and it has been implicated in a variety of inflammatory responses. Over the regions used as immunogen, human and mouse PAR1 proteins are 58% identical in the region spanning the propeptide and extracellular domains, and 84% identical in the cytoplasmic tail.